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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glViewport">
<refmeta>
<refmetainfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
</refmetainfo>
<refentrytitle>glViewport</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glViewport</refname>
<refpurpose>set the viewport</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glViewport</function></funcdef>
<paramdef>GLint <parameter>x</parameter></paramdef>
<paramdef>GLint <parameter>y</parameter></paramdef>
<paramdef>GLsizei <parameter>width</parameter></paramdef>
<paramdef>GLsizei <parameter>height</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<!-- eqn: ignoring delim $$ -->
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>x</parameter></term>
<term><parameter>y</parameter></term>
<listitem>
<para>
Specify the lower left corner of the viewport rectangle,
in pixels. The initial value is (0,0).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>width</parameter></term>
<term><parameter>height</parameter></term>
<listitem>
<para>
Specify the width and height
of the viewport.
When a GL context is first attached to a window,
<parameter>width</parameter> and <parameter>height</parameter> are set to the dimensions of that
window.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
<function>glViewport</function> specifies the affine transformation of
<inlineequation><mml:math><mml:mi mathvariant="italic">x</mml:mi></mml:math></inlineequation>
and
<inlineequation><mml:math><mml:mi mathvariant="italic">y</mml:mi></mml:math></inlineequation>
from
normalized device coordinates to window coordinates.
Let
<inlineequation><mml:math>
<!-- eqn: (x sub nd, y sub nd):-->
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">nd</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">nd</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math></inlineequation>
be normalized device coordinates.
Then the window coordinates
<inlineequation><mml:math>
<!-- eqn: (x sub w, y sub w):-->
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math></inlineequation>
are computed as follows:
</para>
<para>
<informalequation><mml:math>
<!-- eqn: x sub w = ( x sub nd + 1 ) left ( width over 2 right ) + x:-->
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
<mml:mo>=</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">nd</mml:mi>
</mml:msub>
<mml:mo>+</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfenced>
<mml:mo>⁢</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:mi mathvariant="italic">width</mml:mi>
<mml:mn>2</mml:mn>
</mml:mfrac>
</mml:mfenced>
<mml:mo>+</mml:mo>
<mml:mi mathvariant="italic">x</mml:mi>
</mml:mrow>
</mml:mrow>
</mml:math></informalequation>
</para>
<para>
<informalequation><mml:math>
<!-- eqn: y sub w = ( y sub nd + 1 ) left ( height over 2 right ) + y:-->
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
<mml:mo>=</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">nd</mml:mi>
</mml:msub>
<mml:mo>+</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfenced>
<mml:mo>⁢</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:mi mathvariant="italic">height</mml:mi>
<mml:mn>2</mml:mn>
</mml:mfrac>
</mml:mfenced>
<mml:mo>+</mml:mo>
<mml:mi mathvariant="italic">y</mml:mi>
</mml:mrow>
</mml:mrow>
</mml:math></informalequation>
</para>
<para>
Viewport width and height are silently clamped
to a range that depends on the implementation.
To query this range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
<constant>GL_MAX_VIEWPORT_DIMS</constant>.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_VALUE</constant> is generated if either <parameter>width</parameter> or <parameter>height</parameter> is negative.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if <function>glViewport</function>
is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
</para>
</refsect1>
<refsect1 id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_VIEWPORT</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_MAX_VIEWPORT_DIMS</constant>
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glDepthRange</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006
Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see
<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
</para>
</refsect1>
</refentry>